Moss in Linux/macOS

Moss can detect plagiarism in code. It automatically detects program similarity and reports the similar parts in different colors.

Homework Overview

Let assume, you are an instructor or a TA of a course and you want to find the similarities among students' submitted code for a homework assignment. You will use Moss for this job.

In the homework, the students are tasked to solve a problem in Java (or any programming language). Some skleton codes are provided in a few Java files (optional) and the students will write their code on top of that. Finally, each student will submit his/her Java project in a .zip file. The expected directory (package) structure of the project is - Student_Name/src/edu/mystate/cs101/hw1.

Step 1: Setup Environment

1. Perl

   (a) Check Perl is installed

   • Open a terminal and run: perl -v
   • If Perl is installed, you should see output like "This is perl 5 ..."

   (b) If Perl is not installed, install it from terminal

   • sudo apt install perl (Linux)
   • brew install perl (macOS)

2. Python 3

   (a) Check Python 3 is installed on your system

   • Run: python3 --version
   • If Python 3 is installed, you should see output showing the version number, like "Python 3.x.y" (where x and y are any number).

   (b) If Python 3 is not installed, follow the official documentation or read the Python wiki page to install it.

Step 2: Download (or clone) the repository

Download the repo https://github.com/JobayerAhmmed/moss as a zip file and extract it, or clone the repository using git. The directory name will be moss.

Step 3: Register for Moss (doc)

• Send an email to moss@moss.stanford.edu

  • Email subject (optional): registeruser
  • Email body:

  registeruser
  mail <email_address>
  

  • In the email body, replace <email_address> with your email address.

• Copy the content of the reply email after the line:

  --------------------------cut here----------------------

• Save the content to moss.pl file in the moss directory.

Step 4: Download Students' Submissions

• Log in to Canvas and go to the course home page
• Go to Assignments -> Homework 1, (or, homework you want to work on).
• Use the Download Submissions link and download all the student submissions as a .zip file.
• Keep the zip file named as submissions.zip inside the moss directory.

Step 5: Process Submissions for Moss

• Open file main.py from the moss directory.
• Update lines 70-73 in the __main__ section accordingly, if necessary.
• Open a terminal and go to the moss directroy
• Run: python3 main.py

Step 6: Upload Submissions to Moss

• Open a terminal and go to the moss directroy

• To set execution permission, run: chmod +x moss.pl

• To upload to Moss, run:

  • ./moss.pl -l java -d HW1/submissions_for_moss/*/edu/mystate/cs101/hw1/*.java
  • You should change this command according to the changes you have made in the __main__ section of main.py file
    • -l: programming language (i.e., java).
    • -d: submissions are by directory. Files in a directory are taken to be part of the same program and reported matches are organized accordingly by directory (i.e., HW1/submissions_for_moss/*/edu/mystate/cs101/hw1/).

• If the run is success, you will see a message similar to -

  "Query submitted. Waiting for the server's response."

• Wait a few seconds and the Moss will return a URL in the terminal (like: http://moss.stanford.edu/results/2/5294092300784).

• Copy the URL from the terminal and open it in a browser.

• You should see the Moss report for each student's directory.

• Click on a link and it will open the similarity report for the student.